A systematic error in estimating surface-wave group-velocity dispersion curves and a procedure for its correction

A systematic error is known to occur in estimating surface-wave group-veloc ity dispersion when the multiple filter analysis technique is applied. The error comes from the fall-off of the amplitude spectra at long periods. We propose a method for correcting this error. It consists of using a centroid frequency of the filtered spectrum instead of the central frequency of the gaussian window. The method is especially useful when the group-velocity c urve is obtained from stacking of individual frequency-time diagrams. We ap ply this technique to two data sets. The first one consists of nine seismog rams of coastal, subduction-zone earthquakes recorded by a broadband statio n located in Mexico City. This data set has been previously used to estimat e an average crustal structure of southern Mexico. The second data set cons ists of broadband seismograms recorded in India and has been used to determ ine an average structure of the Indian peninsular region. Our results show that, in the first case, the systematic error is negligible. This is due to the relatively low decay rate of the spectral amplitudes at long periods. However, in the case of the Indian data, the systematic error of the multip le filter analysis cannot be neglected since it changes significantly the m easured dispersion curves and leads to errors in the estimated crustal stru cture. Our tests show that the proposed method successfully corrects a majo r part of the systematic error.